The invention relates to a method for producing an adhesive screw connection between at least one upper component and at least one lower component using a flow drill screw.
The invention further relates to a composite component produced according to the invention, which, in particular, is a vehicle body part.
The production of an adhesive screw connection between components by bonding and flow drill screwing is sufficiently known from the prior art. In this respect, reference is made, for example, to German Patent document DE 103 48 427 A1. The process of the non-cutting hole- and thread-forming, as well as a suitable hole- and thread-forming or flow drill screw, are graphically illustrated in German Patent document DE 39 09 725 C1.
Particularly when the upper component has a material thickness and/or hardness unsuitable for flow drill screwing or is made of a material (such as FVK (fibrous composite material that is unsuitable for flow drill screwing, the upper component may have a pre-drilled hole, as illustrated in German Patent document DE 10 2012 210 791 A1. During the screw-in process, the screw tip and, subsequently, also the self-forming thread section of the flow drill screw, impact on the previously applied adhesive layer, causing the adhesive to be swirled up and escape out of the pre-drilled hole. This results in a dirtying of the screw-in device and/or of the components. Furthermore, the adhesive exiting from the pre-drilled hole impairs the torque control of the screw-in device. So far, the screw-in point has therefore been excluded from the application of adhesive. However, the adhesive-free section increases the expenditures for the application of adhesive and results in an interrupted bond seam.
It is an object of the invention to provide a method for producing an adhesive screw connection between at least one pre-drilled upper component and at least one lower component using a flow drill screw, which method does not have the disadvantage associated with the state of the art, or this disadvantage is at least reduced.
The method according to the invention for producing an adhesive screw connection between at least one pre-drilled upper component and at least one lower component using a flow drill screw, which penetrates or extends through the upper component at the joining point through a pre-drilled hole and is screwed together with the lower component while forming a flow hole, provides that the pre-drilled hole in the upper component is covered by a cover (fastened to the upper component) which is first perforated by the flow drill screw before the latter can penetrate into the pre-drilled hole and is subsequently screwed to the lower component.
The method according to the invention is preferably implemented in an automated manner. Several pre-drilled upper components and/or several lower components may be provided. The components are glued to one another on their mutually facing surfaces. The adhesive may be applied over an area or along at least one path (for generating a bond seam).
The cover covering the pre-drilled hole in the upper component prevents an exit of adhesive during the screw-in process. As a result, the components and the screw-in device (including the clamping tools used) cannot be dirtied by escaping adhesive. In addition, if provided, the torque control will remain stable. The application of the adhesive may take place continuously or over the entire surface, which simplifies the application, particularly the automated application, and advantages are also obtained with respect to the achieved strength of the connection and the corrosion behavior at the joining point. The cover also prevents a dirtying of the pre-drilled hole before the screw-in process. Other advantages are also associated with the invention.
A flow drill screw, i.e. a screw suitable for the non-cutting hole- and thread-forming, has a screw shaft with a hole-forming section and a self-forming thread section. The hole-forming section starts from the shaft tip or screw tip and the self-forming thread section adjoins it in the direction of the screw head.
It is preferably provided that the pre-drilled hole in the upper component is a through hole with a circular section. It is preferably provided that the cover covers the entire borehole edge of the pre-drilled hole and, for this purpose, preferably also has a circular design. However, the cover may also have a different shape or a different contour.
The diameter of the cover preferably depends on the diameter of the screw head of the flow drill screw used. In this case, it is particularly provided that the cover has a diameter that is by at least 2 mm larger (radially at least 1 mm) than the screw head of the flow drill screw used. This ensures that, despite the screw-in tolerance (particularly in the case of an automated screwing-in), the screw head does not protrude in the radial direction or project beyond the edge of the cover.
It may be provided, particularly while taking into account the screw head diameter, that the cover has a diameter that results in a radial protrusion of between 1 mm to 8 mm and particularly between 2 mm to 5 mm, with respect to the edge of the pre-drilled hole.
The cover is preferably made of a material that can be perforated in a non-cutting manner by the flow drill screw via contact pressure and rotation. The cover is preferably constructed of a sheet metal material and, particularly preferably, of a steel plate. It may especially be a stamped sheet metal part. The sheet metal material and particularly the steel plate preferably has a thickness of not more than 1.2 mm and particularly of only approximately 0.8 mm. During the perforation of the cover, a flow hole is preferably formed in the cover. The cover may be constructed with a through borehole.
The upper component is preferably made of metal, preferably of a sheet metal material and particularly of steel plate and, in particular, has a thickness (at the joining point) of more than 1.2 mm. The cover, particularly made of metal, can be glued to the upper component, the gluing-together taking place in the projecting area. The fastening of the cover may also take place by contact pressure, for which particularly the cut grade on a cover constructed as a stamped part can be utilized for an interlocking pressing-on or pressing-together with the upper component. It is preferably provided that the cover is welded onto the upper component or is fixed to the upper component by welding. The welding-together preferably takes place by projection welding or friction welding.
The upper component may also be made of a fiber-reinforced plastic material, for example, particularly of glass-fiber-reinforced plastic material (GFRP) or carbon-fiber-reinforced plastic material (CFRP). Analogously to the preceding explanations, the cover can be glued or pressed on.
The lower component is preferably constructed of a material suitable for forming a flow hole, particularly of a steel plate material or aluminum sheet material, having a material thickness or sheet thickness suitable for flow hole forming.
The fastening of the cover to the upper component has to be concluded at the latest before the start of the screwing process. The fastening of all covers preferably takes place immediately following the pre-drilling operation, in which case, this may also be carried out by the supplier.
A composite component according to the invention includes at least one pre-drilled upper component and at least one lower component. These components are joined in at least one joining point via an adhesive screw connection established according to the invention such that the screw shaft of the flow drill screw penetrates or extends through the upper component through a pre-drilled hole and is screwed into the lower component. The perforated cover acts as a washer for the screw head, for which the washer is permanently clamped in between the bottom side of the screw head and the exterior side of the upper component facing the screw head. The composite component particularly is a vehicle body part.
The cover originally intended for covering the upper pre-drilled hole in the top component therefore has a more extensive function as the head washer. The head washer or cover can therefore act as a sealing device, particularly also when the screw is set at a slant, in order to prevent the penetration of corrosive media into the pre-drilled hole and/or an under-head gap. In addition, the surface pressure exercised by the screw head upon the exterior side of the upper component can be reduced or equalized. The cover is preferably constructed of a softer material than the screw material and/or than the material of the upper component.
The composite component according to the invention may have several upper pre-drilled components and/or several lower components. The upper component and particularly also the lower component are preferably constructed in the form of a metal sheet.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawing.